Why are there still no MagSafe car chargers/adapters?

[Racer X]

I saw that one BGnR, but I was wondering if you have a MBP with a 90 watt PS, wouldn't you be running the inverter at 110% load continuously? It does have some extra capacity for shorter periods of time, but wouldn't it eventually overheat?

Now, a MacBook has a 60 watt PS, so it would be OK.

and thermarest, I don't think I have ever seen an inverter below 50 watts. I could see a cheap no name 130 watt one for $20 from a place like target.